1. Field of the Invention
The present invention relates to a method for forming a resist pattern, an overlying layer material and a semiconductor device used in a method for forming a resist pattern. More specifically, the present invention relates to a method for forming a resist pattern, where a process with a high level of environmental resistance has been established, and using an improved overlying layer material for obtaining a pattern having uniform and accurate dimensions, and having a high resolution; and to such an overlying layer material, and to such a semiconductor device.
2. Description of Related Art
In the excimer resist process using an excimer laser for exposure, chemical amplification type resists have been developed and manufactured as the mainstream for both positive and negative resists. These chemical amplification type resists are classified into two types: the type containing an acid forming agent, and the type containing a photo base generator. Either type of resists generates an acid or a base by exposure, and a catalyzed reaction occurs by heat treatment after exposure (post-exposure baking, PEB).
The type recently being developed is the type containing an acid forming agent. Generally in this type containing an acid forming agent, a positive resist comprises a base resin in which the polar group of an alkali-soluble resin is protected by a dissolution inhibiting group, and an acid forming agent; and a negative resist comprises a base resin, a cross-linking agent, and an acid forming agent. This resist containing an acid forming agent undergoes a reaction catalyzed by the acid formed by exposure. In case of the positive resist, the polymer protective group of the base resin is decomposed to be alkali-soluble for the developing solution, and in case of the negative resist, the cross-linking agent reacts with the polymer to increase the molecular weight, becoming insoluble in the developing solution. As a result, a resist pattern is formed. As described above, since the reaction is catalyzed by an acid, the reaction efficiency becomes high, and high sensitivity can be achieved. On the other hand, because of the high environment dependency of the clean room, if the time between exposure and PEB is long, the acid is deactivated by the effect of basic components of the air in the clean room, such as ammonia, raising a problem of the formation of less soluble surface layer in the positive resist. In order to solve this problem, the development of resist materials little affected by basic components of the air has been studied by making applying, exposing, and developing processes in-line.
Concurrent with the above-described development, the process in which an acidic overlying layer material is applied has also been studied for preventing the diffusion of basic components in the resist. The purpose of applying the overlying layer material also includes the improvement of dimensional accuracy. Since the multiple reflection of light beams occurs in the resist film, the dimension of the resist is varied if the thickness of the resist film is uneven. If the underlying layer has steps, the thickness of the resist film is varied, resulting in a significant change in the dimension of the resist pattern. Therefore, the development of the overlying layer material that can inhibit the multiple interference of light beams in the resist film has become essential.
FIGS. 4A through 4E show the process flow of resist pattern formation using a conventional overlying layer material. In FIGS. 4A through 4E, the numeral 10 is a substrate, 12 is a resist applied on the substrate 10, 40 is light beams for exposure, 12a is an exposed part exposed by light beams 40, 12b is an unexposed part not exposed by light beams 40, 14 is an overlying layer material applied on the resist 12, 20 is an acid A contained in the overlying layer material 14, 16 is a mask, and 17 and 18 are film edges formed on the surface of the resist 12.
Referring to FIG. 4A, a resist 12 is applied on a substrate 10, and subjected to a pre-baking treatment. Next, as FIG. 4B shows, an overlying layer material 14 is applied on the resist 12, and subjected to a re-baking treatment. As FIG. 4C shows, light beams 40 are radiated onto the resist 12 through a mask 16, and as FIG. 4D shows, a heat treatment (PEB) after exposure is performed. Finally, by developing the resist 12, resist patterns shown in the left of FIG. 4E are formed in case of the positive resist, and resist patterns shown in the right of FIG. 4E are formed in case of the negative resist.
In order to apply the above-described resist pattern forming process using the conventional overlying layer material to a presently mainstream chemical amplification type resist containing an acid forming agent, the basic components in the air must be trapped. Therefore, the overlying layer material is typically an acidic film. As a result, in case of a positive resist, acid A (20) in the overlying layer material 14 is diffused into the unexposed part 12b of the resist 12 during the PEB treatment after exposure, raising the problems of the formation of film edges 17 on the surface of the unexposed part 12b of the resist 12 caused by the polymer elimination reaction, and the deterioration of the resist patterns. In case of a negative resist, acid A (20) in the overlying layer material 14 is diffused into the unexposed part 12b of the resist 12, a cross-linking reaction occurs also in the unexposed part 12b, and a surface layer difficult to dissolve is formed as shown by the film edges 18, raising a problem that the desired resist pattern cannot be obtained. When this phenomenon is significant, there is a problem that the surface of the resist becomes entirely insoluble. Furthermore, in case of a negative resist, there is a problem that an acidic overlying layer material 14 containing an acid A (20) does not match with the resist 12, and the pattern is degraded or is not resolved.
The object of the present invention is to solve the above problems, and to provide a method for forming resist patterns, an overlying layer material and a semiconductor device used in the method for forming resist patterns, which can inhibit the multiple interference of light beams within a resist film and the uniformity of the dimensions of the resist patterns can be improved, even if the underlying layer has steps and the thickness of the resist film is varied.
Another object of the present invention is to provide a method for forming resist patterns, an overlying layer material and a semiconductor device used in the method for forming resist patterns, which can avoid the effect of basic components such as ammonia in the air in a clean room or the like in applying, exposing, and developing processes, and can inhibit the diffusion of basic components into the resist and improve the environmental resistance of the resist.
A further object of the present invention is to provide a method for forming resist patterns, an overlying layer material and a semiconductor device used in the method for forming resist patterns, which can prevent the diffusion of acids in the overlying layer material into the resist and can obtain resist patterns having rectangular sectional shapes.
According to a first aspect of the present invention, there is provided a method for forming a resist pattern, comprising the steps of: pre-baking a semiconductor substrate on the surface of which a resist has been applied; re-baking the semiconductor substrate, forming a film on the resist using an overlying layer material containing a water-soluble acid substance and a water-soluble photo base generator; post-baking the semiconductor substrate after exposing the overlying layer material to light beams; and forming a resist pattern, developing the resist using a predetermined developing solution and peeling off the overlying layer material together with the developing solution.
According to a second aspect of the present invention, there is provided a n overlying layer material used in a method for forming a resist pattern by pre-baking a semiconductor substrate on the surface of which a resist has been applied; forming a film on the resist using a predetermined overlying layer material, and re-baking the semiconductor substrate; after exposing the predetermined overlying layer material to light beams, post-baking the semiconductor substrate; and developing the resist using a predetermined developing solution, and peeling off the overlying layer material together with the developing solution, wherein the overlying layer material contains a water-soluble acid substance and a water-soluble photo base generator.
According to a third aspect of the present invention, there is provided a semiconductor device used in a method for forming a resist pattern comprising: a semiconductor substrate; a resist applied to the semiconductor substrate; and a film formed on the resist using an overlying layer material containing a water-soluble acid substance and a water-soluble photo base generator.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of the embodiments thereof taken in conjunction with the accompanying drawings.